Collision avoidance system which compares relative velocity vector magnitude with range between two craft

ABSTRACT

A collision avoidance system utilizes only the parameters of course, velocity and range for surface craft and only the parameters of course, velocity, range, and altitude for aircraft. Time to collision is considered equal to the time to the point of nearest approach when the range between two craft falls below a predetermined value. Range to the point of closest approach is not required to determine that a collision hazard exists. No directional antennae are utilized.

hazard exists. N o directional antennae are utilized.

TRANSMITTER ADDER COUNTER EQUALIZER 2 SQUARER E'WR RECEIVER N- S I 2Q? Ns A0051 7 SQUARER V MULTIPLIER CONSTANT l TRIGGER RECEIVER COMPARATOR gGENERAggR l COMPARATOR l RANGE SQUARE GENERATOR TIMING GENERATOR OTRANSMITTER Y7 0 United States Patent 1 3,582,626

[72] Inventor Thomas A. Stansbury [56] References Cited Suite 3242 20 N.Wacker Drive, Chicago, UNITED STATES PATENTS 22 2,385,334 9/1945 Davey235/189 1 PP 85 1969 3,071,767 H1963 Freedman 343/1124 F'led 3,095,5666/1963 Oethloff 343/! l2.4 Division ofber. \0. 273,219. April 15. 1963,3 H4 147 2/1963 Kuecken 343/1 4 d "i' ;g 3,208,064 9/1965 Morrel343/1124 [451 3,227,862 H1966 Freedman 343/1124 Primary Examiner-MalcolmA. Morrison [54] COLLISION AVOIDANCE SYSTEM WHICH AssistantExaminer-Joseph F. Ruggiero COMPARES RELATIVE VELOCITY VECTOR 5 ZgfgRANGE BETWEEN Two ABSTRACT: A collision avoidance system utilizes onlythe 14 CI i 5 D i F parameters of course, velocity and range for surfacecraft and 8 only the parameters of course, velocity, range, and altitudefor [52] U.S. Cl 235/1502, aircraft. Time to collision is consideredequal to the time to 235/ 150.23, 343/112 the point of nearest approachwhen the range between two Q1) l 1 1t Cl 9%;7/78 craft falls below apredetermined value. Range to the point of [50] Field of Search 235/150.2, closest approach is not required to determine that a collisionPATENTEUIIIII IIQII 3.582526 SHEET 1 [IF 2 TRIGGER I 4 5 E? 1 IALTIMETER ENCODER Al COMPASS gg' g 'ZEL TRANSMITTER .ZJ ENCODER TVELOCITY mD'CATOR ENCODER MULTIPLIER N s.

A2 ALTIMETER ENCODER SINE a 1% COMPASS COSNE MULTIJI/EER E 2, TRANSMTTERI 211 ENCgZER L u 725 VELOCITY ENCODER MULTIPLIER IN0Ic9 T oR 124 E'WRDIVIDER lN-S 42 1 ADDERQI N6 '"CONVERTER P RECEIVER R I 30 31 TIMING Q4GENERATOR I 33 COUNTER TRANSMITTER L p 4; 3.2

INVENTOR W EQUALIZER M fifi PATE'NTE BJUN I'ISII 3.582.626

SHEET 2 [IF 2 ALTIMETER ENCODER A2 21 O 2 1 SM a COMPASS b COSINEMULTEL'ER 5W2 TRANSMITTER 2]] T ENCODER co D Z v VELOC'TY 2 ENCODERMULTIPLIER ZS 22. 2 4

I TRIGGER ADDER 2 RECEIQVER 1 E WR SQUARE'R R 'ADDER N-s? IADDERRECEIVER s V & f

' l R VI: i g E MULTlPLlER c 230 M couNTER 24 -'CV CONSTANT COMPARATOREQUALIZER Q0 gg RANGE P Ra a $3 26 4. TIMING TRANSMITTER GENEEZA4TOR A.2:22 i

RELATIVE RELATIVE BEARING BEARING INVENToR 2 fiWmKZ-S/fivnmg COLMSSGNAVOHDANCE SYSTEM Wliilltlilli COMIAlRlES RELATWE VELOCETY VECTGKKMAGNHTUDE WITH RANGE BETWEEN TWG CRAFT This application is a divisionalapplication of my application Ser. No. 273,2l9, filed Apr. 15, l963 nowUS. Pat. No. 3,469,079 issued Sept. 23, 1969.

The present invention relates to navigational aids and more particularlyto systems and methods for preventing collisions between moving craftand stationary obstacles. In the aircraft field, the need fordeviceswhich will aid in the prevention of collisions between aircraft andbetween aircraft and stationary obstructions such as mountainous terrainand tall towers has become well recognized. In becoming betterrecognized, the need for two distinct types of devices has evolved. Thefirst is known as a Pilot Warning Instrument (PWI). It is any deviceproviding the pilot of an aircraft with the relative bearing of anotheraircraft which is a hazard. The Pilot Warning Instrument is primarilyuseful under visual flight rule conditions because it merely gives thepilot the relative bearing of another aircraft so that he may visuallyobserve it, and, from his observation, make whatever decision he feelsis appropriate to avoid a potential collision. The second type of deviceis known as a Collision Avoidance System (CAS). It detects the presenceof potential collision hazards in the form of other aircraft orstationary obstacles, computes the relative movement of the hazard, andprovides the pilot with instructions for avoiding the hazard. TheCollision Avoidance System may also include circuits for issuing controlsignals to an automatic pilot so that any collision avoidance actionwhich the collision avoidance system calculates may be carried out via adirect autopilot connection without requiring any action on the part ofa pilot.

A number of Pilot Warning Instruments and Collision Avoidance Systemshave been developed, but all thus far developed have had limitationswhich have made them impractical for use in general aviation. Thepresent invention overcomes these past limitations and provides both aPilot Warning Instrument and a Collision Avoidance System. One of theprincipal problems in these systems is that of obtaining a practicaldirectional antenna which can obtain bearing information of hazards. lnattempting to avoid the need for a directional antenna, a ground bounceradiation technique has been developed wherein the time lag of areflected RF pulse behind a directly received pulse from a transmitteris measured. However, this technique is severely limited in that itcannot be utilized at low altitudes where the danger of aircraftcollision is highest. The present invention overcomes the requirementfor a directional antenna by providing a position warning indicatorwherein relative bearings of hazards are computed without the use of adirectional antenna and a collision avoidance system which is operableat all altitudes without requiring relative bearing information of thehazards involved.

It is, therefore, an object of the present invention to provide a newand improved navigational aid.

Another object is to provide a Pilot Warning Instrument wherein bearinginformation of a hazard is obtained without the use ofa directionalantenna.

A further object is to provide a collision avoidance system which doesnot require bearing information of a collision hazard and is usable atall altitudes.

Yet another object is to provide a Pilot Warning Instrument whichderives the relative velocity vector direction between two craft byobtaining the velocity vectors of both craft and computing the relativevelocity vector direction.

A still further object of the present invention is to provide aCollision Avoidance System which calculates the probability of acollision from the velocity vectors of two craft to obtain a relativevelocity vector magnitude and comparing it with the range between thetwo craft.

Further objects and advantages will become apparent from the followingdetailed description taken in connection with the accompanying drawings,in which:

FIG. I is a schematic diagram of a preferred form of transmission devicein accordance with the present invention for either a Pilot Warninginstrument or a Collision Avoidance System;

FIG. 2 is a schematic diagram of a preferred form of a Pilot WarningInstrument installation in accordance with the present invention;

FIG. 3 is a schematic diagram ofa preferred form ofa Collision AvoidanceSystem installation in accordance with the present invention;

FIG. 4 illustrates the trigonometry of a typical state of circumstanceswhich may lead to the collision of two craft; and

FIG. 5 illustrates the trigonometry of a typical state of circumstanceswhich do not lead to the collision of two craft.

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail, embodiments of the invention with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciple of the invention and is not intended to limit the invention tothe embodiments illustrated. The scope of the invention will be pointedout in the appended claims.

The present invention encompasses both a Pilot Warning Indicator and aCollision Avoidance System which utilize a common transmission devicefor each craft which may be utilized in either a Pilot WarningInstrument installation or a Collision Avoidance System to perform therespective functions of each type of device. Thus, all craft cooperatingto utilize the present invention would be equipped to carry thetransmission device illustrated in FIG. 1 in order that all wouldtransmit required information, and each craft, at its option, couldutilize either or both the Pilot Warning Instrument installation shownin FIG. 2, or the Collision Avoidance System installation shown in FIG.3. Thus, a craft could participate in a general collision avoidancesystem by merely carrying the transmitter portion of FIG. 2, or it couldobtain desired collision avoidance information from either a Pilotposition Warning Instrument installation indicator or CollisionAvoidance System installation, or if both types of collision avoidanceinformation are desired, it could carry a combined Pilot WarningInstrument and Collision Avoidance System installation. Thus, the costand complexity of the equipment installed in each craft may be tailoredto the speed, maneuverability and type of collision avoidanceinformation desired to be obtained aboard the craft.

Referring now specifically to the transmission device illustrated inFIG. I, a precision altimeter 10, a compass 1 l, and a velocityindicator 12 are connected respectively to a binary encoder 20, a sineand cosine binary encoder 21 and a binary encoder 22 in order togenerate the altitude of a first aircraft, its heading or course bynorth-south and east-west components and its velocity in the form of abinary code. The compass ll may be any form ofa high accuracy compasssuch as a gyro compass or a flux gate compass. A binary multipliercircuit 23 is connected to encoder 21 to receive a binary code signalindicative of the sine of the heading of the aircraft and to encoder 22to receive a signal indicative of the velocity of the aircraft. Theseare combined in multiplier 23 to produce an east-west velocity vectorcomponent in the form of a lO-bit binary word. In a similar matter, amultiplier 24 is connected to encoder 21 to receive a binary signalindicative of the cosine of the heading and is connected to encoder 22to receive the signal indicative of velocity to calculate a 10-bitnorth-south velocity vector component. A telemetering-type transmitteris connected to the encoder 20, multiplier 23, and multiplier 24 toplace the three IO-bit binary code signals of altitude A the east-westvelocity vector E-W and the northsouth velocity vector N-S, onsubcarriers which are, in turn, modulated on the carrier wave generatedby the transmitter. The RF oscillator generating the carrier wave isconnected to the altimeter 10 in order that the frequency of thetransmitter may be varied in accordance with the altitude as the craftclimbs and descends. The transmitter 25 is connected to anomnidirectional antenna 26 for the purpose of radiating the carrier wavewith its three subcarriers in pluses each being sufficiently long tocontain the lO-bits of binary code on the sub carriers. Thus, theradiated signal contains a general indication of altitude in thefrequency of the carrier wave and also a more specific altitude signalin the lO-bit binary code modulated on the first subcarrier A triggerreceiver 27 is connected to an omnidirectional antenna 28 mounted on thefirst aircraft, to receive interrogation pulses from other craft, andconnected to transmitter 25 to trigger it when an interrogation pulse isreceived from another craft. Whenever transmitter is so triggered, itemits through antenna 26 one pulse containing the three binary codesignals of altitude, east-west component and north-south component onthe subcarriers. The equipment thus far described as installed in afirst craft completes a minimum station when so installed in a craft toallow it to be recognized by other craft equipped with a system as isillustrated either in FIGS. 2 or 3.

Referring now to FIG. 2, a second aircraft is equipped with a PWlinstallation which not only transmits signals containing altitude andvelocity vector component information, but also receives suchinformation from other aircraft in order to compute the magnitude of therelative velocity vector between itself and the other aircraft. Itincludes an altimeter 110, a compass H1, and a velocity indicator 112connected to a set of binary encoders 120-122 which are equivalent toaltimeter J10, compass 11, velocity indicator l2, and encoders 20-22,respectively. Binary multipliers 23 and 24 are connected to encoders 121and 122 in a manner similar to multipliers 23 and 241 to produce theeast-west E-W and north-south N-S velocity components of the velocityvector of this second craft. A telemetering transmitter 125 and triggerreceiver 127 perform the same functions as telemetering transmitter 25and trigger receiver 27 in securing altitude and velocity componentinformation and radiating it in the form of a carrier with threesubcarriers through an antenna 126 when an interrogation pulse isreceived on antenna 128.

An omnidirectional receiving antenna 30, mounted on the second craft, isconnected to a telemetering-type receiver 31 which receives anddemodulates the subcarriers of a pulse signal from antennas 26 if thefirst craft is radiating a carrier wave which has a frequency which isindicative of an altitude within several thousand feet of the altitudeindicated by altimeter 1110 on the second craft. Altimeter 110 isconnected to receiver 311 to control a band-pass tuning control of thereceiver so that altitude signals which are indicative of altitudeswithin several thousand feet of the altitude indicated by altimeter 110pass through a variable band-pass tuning filter. Those that do pass havethe binary code on the three subcarriers demodulated. Thus, thefrequency of the radiated carrier wave and the tuning of the band-passfilter and telemetering receiver 31 prevent the Pilot Warning Instrumentinstallation from beingjammed by an excessive number of transmissionswhich are received simultaneously. The formula for computing thedirection of the relative velocity vector between the first and secondcraft is:

(l', sin a-l' sin b) O-arc tan (V cos al' cos b) (1) where:

V is the magnitude of the velocity vector of the first craft;

V is the magnitude of the velocity vector of the second craft;

a is the heading of the first craft;

b is the heading of the second craft; and, therefore,

V sin a is the east-west velocity component of the first craft E-W,;

V, cos a is the north-south velocity vector of the first craft N-S V sinb is the eastwest velocity vector of the second craft E-W and V cos b isthe north-south velocity vector of the second craft N-S Those skilled inthe art are familiar with the fact that if two craft are on a potentialcollision course, that the relative bearing of the one craft from theother will remain constant. When the bearing of another craft remainsconstant, the direction of the relative velocity vector between the twocraft coincides with the constant relative bearing. If the direction ofthe relative velocity vector differs slightly from the relative bearing,the two craft will have a near miss. The present invention utilizes thefact that the direction of the relative velocity vector is approximatelyequal to the relative bearing between the two craft whenever there is aprobability of a collision or a near miss between the two craft. Thusindicating the direction of the relative velocity vector to a pilot ofone craft is equivalent to indicating the approximate bearing of theother craft. When he has been given this information, he may immediatelyvisually turn his attention to that approximate bearing to effect animmediate visual contact with the first craft. A typical collisionsituation is illustrated in FIG. 4, and a typical near miss situation isillustrated in FIG. 5. Whenever there is a large variance between therelative bearing of one aircraft from another and the direction of therelative velocity vector between them, no possibility of even anear misswill exist. However, for two aircraft to arrive anywhere in the vicinityof each other, they must, of necessity, be either on steady courseswhich will eventually bring them into either a collision situation or anear miss situation. Even in the situation where aircraft are changingtheir headings, frequently such as in a situation where one or both areexecuting various acrobatic type maneuvers, their average velocityvector over a period of time must be such that they are brought closertogether. When two craft finally arrive at a sufficiently short rangethat either further maneuvering or the courses which they are makinggood at that time will bring them into a collision situation, the pilotof at least one and preferably both aircraft should be warned and givena bearing for visual contact of the other craft. In order to eliminatethe situation of two craft actuating an alarm portion of the PWl whenthe two craft are far apart and thus may never be a hazard to oneanother, the transmission device illustrated in FIG. 1 has its antenna28 for receiving interrogation signals connected to the triggergenerating receiver 27, which is, in turn, connected to transmitter 25to trigger it whenever it receives an interrogating pulse asaforementioned. The system illustrated in FlG. 2, on the secondaircraft, includes an interrogating transmitter 32 connected to anomnidirectional antenna 33, which periodically emits triggering pulseswhich are received by antenna 28, These signals are transmitted bytransmitter 32 in accordance with timing pulses received from timinggenerator 34. The timing generator 34 sends a trigger pulse totransmitter 32 and then allows sufficient time for reply data signals tobe received from all aircraft within a dangerous range to be received bytelemetering receiver 31. By so limiting the range of received datasignal, the possibility of the PWl giving a false alarm is reduced to apractical minimum, and at the same time, situations wherein the relativevelocity vector is not within a few degrees of the relative bearingbetween two aircraft, is practically eliminated. The danger range mayvary from about 3 miles for a small, low-speed aircraft to the order of30 miles for a highspeed jet.

The multipliers 123 and 124 provide the east-west E-W and thenorth-south N-S velocity components of the second aircraft. Thesequantities are available to a pair of convention binary adders 40 and41, respectively, which are constructed for substraction. These addersperiodically receive and store the velocity components of the secondaircraft through suitable connections. They are connected to thereceiver 31 so that when a signal is received from the second aircraft,the receiver 31 demodulates the velocity vectors of the first aircraftand sends east-west component to adder 40 to substract it from the firstaircrafts east-west component and sends the first aircrafts north-southcomponent to adder 41 to subtract it from the second aircraft'snorth-south components. Thus, the adder 40 provides a resultant signalto a conventional binary divider 42 which is the east-west component E-Wof the relative velocity vector between the first and second aircraft,and adder 411 provides a signal to divider 42 which is the northsouthcomponent N-S of the relative velocity vector between the two craft. Thedivider 42 provides the necessary division, as indicated in formula (l)to provide tangent 0 to a tangent converter 43 which, in turn providesthe angle 6 to a display unit 454. The display unit 445 is a binary todecimal type display having a multiple of decimal units so that thedirection of the relative velocity vector between the two aircraft isvisually displayed as a decimal number and retained for a predeterminedperiod of time. Thus, a pilot of the second craft is made aware of thehazard, and he has time to read the display to obtain the necessaryapproximate relative bearing of the hazard. The display alsoincorporates an audio or visual alarm which attracts the pilot'sattention to the fact that information from a potential hazard has beenreceived.

In order to eliminate aircraft which are not cruising within 1,000 feetof the second aircraft, an additional altitude circuit is provided whichconsists of a binary 3-bit counter 45 and a binary equalizer 46 whichare connected to the receiver 31 to receive the binary coded altitudesignal which is a standard binary code giving altitude above sea levelat intervals of 100 feet. Each time a new code signal is received,counter 45 counts off the first three bits, and during this time, sendsa signal to equalizer 46 which disables it during this period of time.Equalizer 46 is connected to the binary encoder 120 which is connectedto altimeter 110 to encode the altitude of the second aircraft in binaryform. The equalizer 46, upon receiving an altitude code signal fromreceiver 31, being held inoperable during the first three bits bycounter 45, is unable to compare the first three bits of the receivedencoded signal with the first three hits of the second aircraft encodedsignal. Beginning with the fourth bit of both the first and secondaircraft altitude codes, the equalizer compares the bits to determinewhether they are similar. If the remaining seven bits of the lO-bit codeare each respectively similar, indicating equal altitudes within therange of 1,400 feet, the equalizer 46 produces an actuation signal on anoutput terminal which is connected to the alarm circuits in the displayunit 44 so that they will be actuated only when they receive both theangle 6 indication signal from the divider 42 through the converter 43and the actuation signal from the equalizer as.

Referring now to FIG. 3, a Collision Avoidance System in stallation isillustrated in which components which are similar to the componentsfound in the transmission device illustrated in FIG. 1, and the PilotWarning instrument illustrated in FIG. 2, have corresponding numbers.For the purpose of illustration, it is assumed that this installation isinstalled in the second aircraft rather than the installation shown inFIG. 2. It will be observed that the transmission device is similar tothat illustrated in FIGS. 1 and 2. It operates in the same manner aspreviously described for the transmission device (10-28) of P16. 1 andthe transmission device portion (110-128) of FIG. 2. An altimeter 210has an output which is encoded by an encoder 221 into the l0-bit binaryaltitude code; a compass 211 has an output connected to a sine andcosine encoder 222 to provide the sine of the aircraft heading b to amultiplier 223 and a cosine function of the aircraft heading b to amultiplier 224, and a velocity indicator 212 has the second aircraftsvelocity V encoded by an encoder 223 to provide the binary code to bothmultipliers 223 and 224. In order to modulate the subcarriers or carriersignal pulses transmitted by a data transmitter 225 in binary code withaltitude A east-west velocity vector of the aircraft's velocity E-W andnorth-south velocity vector of the aircraft velocity vector N-S encoder221, multiplier 223 and multiplier 224 are connected to transmitter 225.Carrier signal pulses are radiated from an antenna 226. For the purposeof triggering the carrier pulses containing this information forreception by other aircraft, an antenna 228 is connected to a triggerreceiver 227, which is, in turn, connected to the data transmitter 225to trigger the carrier pulse which has the altitude and the east-westand north-south components of the aircraft's velocity vector modulatedthereon.

For the purpose of receiving such information from aircraft similarlyequipped, a trigger transmitter 232 is connected to a timing generator234 in order to periodically trigger the transmitter 232 to transmitinterrogation pulses through its antenna 233. The interrogation pulsesare such as the first aircraft which send a reply information pulsethrough a data transmitter such as 25, and 225 with the altitude andrelative velocity west-east and north-south components modulated onsubcarriers. An antenna 230 receives such signals. A data receiver 231demodulates the altitude binary code, and the east-west and north-southvelocity vectors. An adder 240 is connected to the data receiver forreceiving the east-west velocity vector E-W, of another aircraft whichagain is assumed to be the aforementioned first aircraft, and to themultiplier 223 for receiving the cast-west velocity vector E-W of thesecond aircraft in order to algebraically add these eastwest velocityvector components together and provide the resultant component E-W to aconventional binary squarer circuit 51. In a like manner, an adder 241is connected to the data receiver 231 to receive the north-southvelocity vector component N-S of the first aircraft and to themultiplier 224 to receive the north-south velocity vector component N-S,of the second aircraft to provide a resultant north-south velocityvector component N-S to a conventional binary squarer circult 52. Abinary adder 53 is connected to the squarer circuit 51 to receive abinary code signal representing a square of the east-west component ofthe relative velocity (E-W and to the squarer circuit 52 to receive abinary code signal representing the north-south component of therelative velocity (N-S between the two aircraft. The binary adder 53adds the squares of the two rectangular components to produce a binarycode signal which is the relative velocity of the two aircraft squaredV,,.

The demodulated altitude signal A in the form of a binary code istransferred from the data receiver 231 to a three bit counter 245, to anequalizer 246 and to a binary code comparator 54. The three bit counter245 is connected to the equalizer 246 to transfer a signal to theequalizer 246 which allows it to commence its equalizing function ofcomparing the altitude of the second aircraft with the altitude of thefirst aircraft after the first three bits have passed, which, in effect,compares the altitude of the two aircraft to determine whether they arewithin 1,400 feet of each other. The equalizer 246 is connected to theoutput of the encoder 221 to receive the 10- bit altitude coderepresenting the altitudes of the second aircraft. If the two aircraftare found to be within l,400 feet of each other, as determined byequalizer 246, a signal is generated which is transferred through aconnection to a display unit 55, which will activate the display unit55, as will presently be described in greater detail. The comparator 54is similarly connected to the output of the encoder 221 to receive thesecond aircraft's altitude in addition to the first aircraft's altitudein order to compare them and determine which aircraft is above theother. The comparator 54 is connected to the display unit 55 for thepurpose of sending, either a signal which indicates that the secondaircraft is above the first aircraft, or a signal indicating that it isbelow the first aircraft.

The timing generator 234 issues a timing trigger pulse to a range squaregenerator 56 at the same time it issues a trigger pulse to the triggertransmitter 232 so that the range square generator commences to generatea binary code signal r which is equal to the square of the range betweenthe second aircraft and the first aircraft from which a reply signal isreceived on antenna 230.

A constant generator 57 which generates a constant binary code signal Cand an output of the adder 53 are both connected to a conventionalbinary multiplier 58 to produce a signal CV, which is equal to therelative velocity squared multiplied by the constant C.

An output of the adder 53 is connected to a comparator 60 and an outputof the range square generator 58 is also connected to the comparator 60in order that the comparator may compare the binary code signal whichrepresents the square of the range between the two craft r and thebinary code signal of the constant and the square of the relativevelocity between the two aircraft at that moment CV If the constanttimes the square of the relative velocity CV is greater than the squareof the range r of the comparator 60 issues an actuating signal to thedisplay unit 55. Whenever the display unit 55 receives a signal from theequalizer 246, indicating that another aircraft is within L400 feet ofthe second aircraft, and a signal from the comparator 60 that Cl/ isless than r, it sounds an audio in unit 55 and illuminates either anarrow 61 or an arrow 62 on the face of display unit 55, to indicate thata possible collision is imminent. If the signal from the comparator 55indicates that the first aircraft is below the second aircraft, then thearrow 61 will be illuminated indicating that the avoidance maneuver is aclimb. If the first aircraft is above the second aircraft, the arrow 62is illuminated to indicate that the collision avoidance maneuver is adive.

If two aircraft are actually on collision courses the time Tto the pointof collision is represented by equation (2 T=r/V (2) wherein:

r the range between two aircraft at any given time and V the relativevelocity vector between the aircraft at the given time.

If two aircraft are not on collision courses, T will remain relativelylarge because they will not close the range between them until they area hazard to each other. Therefore, T may be utilized as a measure of thedevelopment ofa potential collision situation. When it reaches arelatively low value, evasion maneuvers should be taken to prevent acollision. This value should be large enough to allow sufficient timefor any one aircraft to take evasive action to avoid a collision even ifthe other involved aircraft does not aid in the evasive action. It mayvary with the performance of the aircraft involved. A value that hasbeen generally accepted in civil aviation to include high performancejet transport aircraft is 45 seconds. Whenever T is equal to or lessthan K, a collision hazard exists between the two aircraft involved. IfIt is made equal to another constant C, then a collision hazard existswhenever C is equal to or greater than T as indicated in equation (3).

C; T RWV (3) Therefore,

C 2 n indicates that a collision hazard exists between two aircraft.This is the criterion utilized by the system illustrated in FIG. 3 todetermine whether a potential collision exists between two givenaircraft. It may be observed that the quantities C, V and r may bealgebraically transposed in any form that will allow a comparison of thethree quantities. For the system illustrated in FIG. 3, the quantitiesare transposed so that CV is equal to or greater than r As illustrated,the east-west and north-south components of the relative velocity areproduced by adders 240 and 241 as they were by the adders 40 and 41 inthe Pilot Warning Instrument system illustrated in FIG. 2. These twocomponents of the relative velocity are squared by the binary squarercircuits 51 and 55 and added algebraically in the adder 53 to accomplishthe following equation of: Z R) R) l 2) 1 2) The range square generator56 provides a continuous output of 1- which is multiplied with theconstant C received from the constant generator 257 in the multiplier258 to produce the quantity CR. As previously mentioned, the comparator260 compares the product C V to r to determine whether the product CV islarger than the square of the range, and if CV is larger than r anactuating signal is issued by the comparator 60 to the display unit 55.Since the display unit 55 is simultaneously receiving a signal from theequalizer 246 to determine whether the other aircraft is within adangerously close altitude of the other aircraft and is receiving arelative comparison of aircraft from the comparator 54, it may utilizeeither the arrow 61 or 62 to warn the pilot to either climb or dive toavoid the other aircraft.

In order to avoid saturating the receiver 231 which contains a variableband-pass filter, it is connected to the altimeter 210, for the purposeof excluding information signals from all aircraft which are at asignificantly different altitude than own aircraft. As a further methodof preventing saturation of the receiver, it is connected to timinggenerator 234 so that it receives a signal from the timing generatorafter a sufficient period of time has elapsed to receive any possiblesignals within the longest possible potential hazardous range of anotheraircraft has elapsed.

If every aircraft operating in a given area of the atmosphere were tocarry either the minimum station illustrated in FIG. ll, the PilotWarning Instrument installation illustrated in FIG. 2, or the CollisionAvoidance System installation illustrated in FIG. 3, all such aircraftwould be able to cooperate with each other. The aircraft carrying theminimum station" of FIG. 1 make their presence and necessary dataavailable to all other aircraft so that they may take steps to avoidthem. The aircraft equipped with the Pilot Warning Instrumentinstallation are able to receive a warning and bearing indication ofhazardous aircraft. The aircraft equipped with the Collision AvoidanceSystem installation are able to react to the collision avoidanceinstructions produced by that system either manually or automatically,for the signals utilized to initiate arrows 61 and 62 may be utilized tocontrol an automatic pilot and cause an aircraft to automatically climbor dive. Since the components of the systems illustrated in the PilotWarning Instrument installation illustrated in FIG. 2 and the CollisionAvoidance System installation illustrated 'in FIG. 3 are similar, exceptfor a relatively few units, a combined Pilot Warning Instrument and aCollision Avoidance System can be provided by connecting the componentsof FIG. 3, not found in FIG. 2, to the appropriate common componentsfound in FIG. 2. Thus, a fourth system is provided which is within thescope of the present invention. Its complexity and weight is onlyslightly greater than either the Pilot Warning Instrument installationor the Collision Avoidance System installation alone.

Although the Collision Avoidance Systems illustrated utilize thetransmission of the north-south and east-west components of each craftsvelocity, which are velocity components perpendicular to each other, thescope of the present invention includes the utilization of the describedinstallations with any preselected pair of perpendicular velocityvectors for the aircraft operating in the system. The scope of thepresent invention also includes the transmission of data by means otherthan perpendicular velocity components such as the direct transmissionof velocity and course or heading between aircraft which may be resolvedat the receiving aircraft into perpendicular components before applyingthem to the special circuits of either the Pilot Warning Instrumentinstallation of the Collision Avoidance System installation. Suchsystems will operate with any or all of the systems specified in mycopending application Ser. No. 448,554, filed Apr. 1, 1965. In suchsystems, the heading or course and the velocity of a first aircraftwould be fed to a rectangular component resolver of any design wellknown to those skilled in the art to provide the perpendicularcomponents. These rectangular components resulting from the resolvercould then be combined with the rectangular components, provided on thesecond craft, as illustrated by FIGS. 2 and 3. Further, in someinstances, it may be desirable to receive course and velocityinformation from a first aircraft and to resolve it into perpendicularcomponents with one component parallel with the heading or velocityvector component of a second aircraft.

Any one of the four types of installations may be utilized inconjunction with a stationary object. The transmitter used for astationary point would emit signals, when triggered, indicating zerovelocity and the altitude of the point.

I claim:

1. A collision avoidance system comprising:

a transmitter on a first craft for generating signals indicative of afirst craft velocity vector,

means on a second craft for generating signals indicative of a secondcraft velocity vector,

a receiver means on the second craft for receiving said signalsindicative of the first craft velocity vector, said receiver connectedto said means of generating signals indicative of a second craftvelocity vector for combining said si nals to determine the magnitude ofa relative velocity vector,

a first computing means on said second craft for determining a rangebetween said first and second craft, and

a second computing means on said second craft connected to said receivermeans and to said first computing means for comparing the magnitude ofthe relative velocity vector determined by said receiver means to therange determined by said first computer means to determine whether ahazardous relationship exists between said first and second craft, saidsecond computer means requiring no other inputs to determine whether ahazardous relationship exists between said first and second craft.

2. A collision avoidance system comprising:

a transmitter on a first craft for generating signals indicative of afirst craft velocity vector and its altitude,

means on a second craft for generating signals indicative of a secondcraft velocity vector and its altitude,

a receiver means on the second craft for receiving said signalsindicative of the first craft velocity vector, said receiver connectedto said means of generating signals indicative of a second craftvelocity vector for combining said signals to determine the magnitude ofa relative velocity vector,

a first computing means on said second craft for determining a rangebetween said first and second craft, and

a second computing means on said craft connected to said receiver meansand to said first computing means for comparing the magnitude of therelative velocity vector determined by said receiver means to the rangedetermined by said first computer means and for comparing said altitudesignals to determine whether a hazardous relationship exists betweensaid first and second craft, said second computer means requiring noother inputs to determine whether a hazardous relationship existsbetween said first and second craft.

3. A collision avoidance system comprising:

a transmitter on a first craft for generating signals indicative of afirst craft velocity vector and its altitude,

means on a second craft for generating signals indicative of a secondcraft velocity vector and its altitude,

a directional receiver on a second craft for receiving said signalsindicative of the first craft velocity vector, said receiver connectedto said means of generating signals indicative of a second craftvelocity vector for combining said signals to determine an approximaterelative bearing of said first craft from said second craft to determinethe magnitude of the relative velocity vector, said directional receiverrequiring no other inputs to calculate the approximate relative bearingof said first craft from said second craft,

a first computing means on said second craft for determining a rangebetween said first and second craft, and

a second computing means on said second craft connected to saiddirectional receiver and to said first computing means for comparing themagnitude of the relative velocity vector determined by said directionalreceiver to the range determined by said first computer means and forcomparing said signals indicative of the first and second craftaltitudes to determine whether a hazardous relationship exists betweensaid first and second craft, said second computer means requiring noother inputs to determine whether a hazardous relationship existsbetween said first and second craft.

4. A collision avoidance system comprising:

a transmitter on a first craft for generating signals indicative ofafirst craft velocity vector,

means on a second craft for generating signals indicative of a secondcraft velocity vector,

Eli

a receiver means on the second craft for receiving said signalsindicative of the first craft velocity vector, said receiver connectedto said means of generating signals indicative of a second craftvelocity vector for combining said signals by squaring their individualvalues and adding the squares together to obtain the square of themagnitude of a relative velocity vector,

a first computing means on said second craft for determining a rangebetween said first and second craft, and

a second computing means on said second craft connected to said receivermeans and to said first computing means to divide the square of therelative velocity vector by a square of the range determined by saidfirst computing means and to determine whether the resultant quotient isless than a predetermined value.

5. In a collision avoidance system, the combination of:

a transmitter generating signals indicative of the rectangularcomponents of a first craft velocity vector,

a receiver means receiving said signals indicative of rectangularcomponents of the first craft velocity vector,

means on said second craft for generating signals indicative of therectangular components of the second craft velocity vector, and

computing means connected to said receiver means and to said secondcraft signal generating means for combining the magnitudes ofcorresponding components indicative of the first and second craftvelocity vectors to determine whether each said craft is a possiblehazard to the other said craft, said computer means receiving no otherinputs to determine whether each said craft is a possible hazard to theother craft whenever the altitude of the two craft are within apredetermined relative range of each other.

6. A system for indicating the presence of a navigational hazardcomprising:

a transmitter adapted to be carried by a first craft for generatingsignals having characteristics indicative of the altitude, course andvelocity of said craft,

a receiver carried by said craft for receiving other signals transmittedfrom a second craft and having characteristics indicative of thealtitude, course and velocity of said second craft,

range measuring means carried by said first craft for determining therange of said second craft, and

means utilizing said signals and said range measuring means to indicatewhether said second craft is a navigational hazard to the first craft,said means requiring no other inputs to determine when said second craftis a navigational hazard to said first craft.

7. A system for indicating the presence of a navigational hazardcomprising:

a transmitter adapted to be carried by a first craft for generatingsignals indicating the actual altitude, course and velocity of saidcraft,

a receiver carried by said craft for receiving other signals transmittedfrom a second craft and indicating the actual altitude, course andvelocity of said second craft,

range measuring means carried by said first craft for determining therange of said second craft, and

means utilizing said signals and said range measuring means to indicatewhether said second craft is a navigational hazard to the first craft,said means requiring no other inputs to determine when said second craftis a navigational hazard to the first craft.

8. A computer comprising:

first means for combining signals representative of a first componentrelative to two fixed orthogonal datum lines of a first crafts velocityvector and a parallel first component of a second craft's velocityvector to obtain a signal representative of a first component of arelative velocity vector having a magnitude,

second means for combining signals representative of a second componentrelative to said fixed orthogonal datum lines of said first craftsvelocity vector which is perpendicular to said first component and aparallel second component of said second crafts velocity vector toobtain a signal representative of a second component of the relativevelocity vector,

third means connected to said first and second means for obtaining asignal representative of the relative velocity vector magnitude from thesignals representative of said first and second relative velocity vectorcomponents, and

fourth means for combining said signal representative of the relativevelocity vector magnitude with a signal representative of the rangebetween said first and second craft to obtain a value representative ofthe time to a point of closest approach between said first and secondcraft, said fourth means requiring no other inputs to obtain the valuerepresentative of the time to a point of closest approach between saidfirst and second craft.

9. A computer comprising:

first means for combining signals representative of a first component ofa first crafts velocity vector and a parallel first component of asecond crafts velocity vector to obtain a signal representative of afirst component of a relative velocity vector having a magnitude,

second means for combining a signal representative of a second componentof said first crafts velocity vector which is perpendicular to saidfirst component and a parallel second component of said second craftsvelocity vector to obtain a signal representative of a second componentofthe relative velocity vector,

third means connected to said first and second means for obtaining asignal representative of the relative velocity vector magnitude from thesignals representative of said first and second relative velocity vectorcomponents,

fourth means for obtaining a signal representative of the range betweenthe first and second craft, and

fifth means connected to said third and fourth means for combining saidrelative velocity vector magnitude and said range to determine whethereach craft is a potential hazard to the other, said fifth meansrequiring no other inputs to determine whether each craft is a potentialhazard to the other.

M. A computer comprising:

first means for combining a signal representative of a first componentof a first crafts velocity vector and a parallel first component of asecond crafts velocity vector to obtain a signal representative ofafirst component of a relative velocity vector having a magnitude,

second means for combining a signal representative of a second componentof a first crafts velocity vector which is perpendicular to said firstcomponent and a parallel second component of said second crafts velocityvector to obtain a signal representative of a second component of therelative velocity vector,

third means connected to said first and second means for obtaining asignal representative of the relative velocity vector magnitude from thesignals representative of said first and second relative velocity vectorcomponents,

fourth means connected to said third means for combining said signalrepresentative of the relative velocity vector magnitude with a signalrepresentative of the range between said first and second craft toobtain a signal representative of the time to a point of closestapproach between said first and second craft,

fifth means for combining a signal indicative of the altitude of saidfirst craft with a signal indicative of the altitude of said secondcraft to determine whether said craft are within a predeterminedaltitude range of each other, and

sixth means connected to said fourth and fifth means for determiningwhether said first and second craft are a hazard to each other, saidsixth means requiring no other inputs to determine whether said firstand second craft are a hazard to each other.

11. A computer comprising:

first means for combining signals representative of a first component ofa first crafts velocity vector and a parallel first component of asecond craft's velocity vector to obtain a signal representative ofafirst component of a relative velocity vector having a direction and amagnitude,

second means for combining signals representative of a second componentof said first crafts velocity vector which is perpendicular to saidfirst component and a parallel second component of said second craft'svelocity vector to obtain a signal representative of a second componentof the relative velocity vector,

third means connected to said first and second means for combining thesignal representative of said first relative velocity vector componentwith the signal representative of said second relative velocity vectorcomponent to obtain a signal representative of the relative velocityvector direction and a signal representative of the relative velocityvector magnitude,

fourth means for obtaining a signal representative of the range betweenthe first and second craft,

fifth means connected to said third and fourth means for combining saidsignal representative of the relative velocity vector magnitude withsaid signal representative of the range between said first and secondcraft to obtain a value representative of the time to a point of closestapproach between said first and second craft, said fifth means requiringno other inputs to obtain a value representative of the time to a pointof closest approach between said first and second craft,

sixth means for combining a signal indicative of the altitude of saidfirst craft with a signal indicative of the altitude of said secondcraft to determine whether said craft are within a predeterminedaltitude range of each other, and

seventh means for determining whether each craft is a potential hazardto the other responsive to said fifth means for obtaining a valuerepresentative of the time to a point of closest approach and responsiveto said sixth means for determining whether said craft are within apredetermined altitude range of each other.

12. A computer comprising:

first means for combining a signal representative of a first componentof a first crafts velocity vector and a parallel first component of asecond craft's velocity vector to obtain a signal representative of afirst component of a first relative velocity vector having a magnitudeand a first component of a second relative velocity vector having amagnitude,

second means for combining a signal representative of a second componentof said first crafts velocity vector which is perpendicular to saidfirst component and a parallel second component of said second craftsvelocity vector to obtain a signal representative of a second componentof the first relative velocity vector,

third means connected to said first and second means for obtaining asignal representative of the first relative velocity vector magnitudefrom said signals representative of said first and second relativevelocity vector components of said first relative velocity vector,

fourth means connected to said third means for combining said signalrepresentative of the first relative velocity vector magnitude with asignal representative of the range between said first and second craftto obtain a signal representative of the time to a point of closestapproach between said first and second craft,

fifth means for combining a signal representative of a third componentof said first crafts velocity vector which is perpendicular to saidfirst and second components to a signal representative of a parallelthird component of said second craft's velocity vector to obtain asignal representative of a second component of the second relativevelocity vector,

sixth means connected to said first and fifth means for obtaining avalue representative of the second relative 4111" Anna velocity vectormagnitude from said signals representative of said first and thirdrelative velocity vector components, and seventh means connected to saidsixth means for combining said signal representative of the secondrelative velocity vector magnitude with a signal representative of therange between said first and second craft to obtain another signalrepresentative of the time to a point of closest approach between saidfirst and second craft. l3. ln combination with the computer specifiedin claim 12, an eighth means connected to said fourth and seventh meansfor determining whether the time to a point of closest approach derivedfrom said signal representative of said first relative velocity vectorand the time to a point of closest approach derived from said signalrepresentative of said second relative velocity vector are less than apredetermined interval of time.

14. A computer comprising: first means for combining signalsrepresentative of a first component of a first craft's velocity vectorand a parallel first component of a second craft's velocity vector toobtain a signal representative of a first component of a relativevelocity vector having a magnitude, second means for combining signalsrepresentative of a second component of said first crafts velocityvector which is perpendicular to said first component and a parallelsecond component of said second crafts velocity vector to obtain asignal representative of a second component of the relative velocityvector,

third means for combining signals representative of a third component ofsaid first craft's velocity vector which is perpendicular to said firstand second components and a parallel third component of said secondcraft's velocity vector to obtain a signal representative of a thirdcomponent of the relative velocity vector,

fourth means connected to said first, second and third means forobtaining a value representative of the relative velocity vectormagnitude from the signals representative of said first, second, andthird relative velocity vector components, and

fifth means connected to said fourth means for combining said signalrepresentative of the first relative velocity vector magnitude with asignal representative of the range between said first and second craftto obtain a value representative of the time to a point of closestapproach between said first and second craft.

1. A collision avoidance system comprising: a transmitter on a firstcraft for generating signals indicative of a first craft velocityvector, means on a second craft for generating signals indicative of asecond craft velocity vector, a receiver means on the second craft forreceiving said signals indicative of the first craft velocity vector,said receiver connected to said means of generating signals indicativeof a second craft velocity vector for combining said signals todetermine the magnitude of a relative velocity vector, a first computingmeans on said second craft for determining a range between said firstand second craft, and a second computing means on said second craftconnected to said receiver means and to said first computing means forcomparing the magnitude of the relative velocity vector determined bysaid receiver means to the range determined by said first computer meansto determine whether a hazardous relationship exists between said firstand second craft, said second computer means requiring no other inputsto determine whether a hazardous relationship exists between said firstand second craft.
 2. A collision avoidance system comprising: atransmitter on a first craft for generating signals indicative of afirst craft velocity vector and its altitude, means on a second craftfor generating signals indicative of a second craft velocity vector andits altitude, a receiver means on the second craft for receiving saidsignals indicative of the first craft velocity vector, said receiverconnected to said means of generating signals indicative of a secondcraft velocity vector for combining said signals to determine themagnitude of a relative velocity vector, a first computing means on saidsecond craft for determining a range between said first and secondcraft, and a second computing means on said craft connected to saidreceiver means and to said first computing means for comparing themagnitude of the relative velocity vector determined by said receivermeans to the range determined by said first computer means and forcomparing said altitude signals to determine whether a hazardousrelationship exists between said first and second craft, said secondcomputer means requiring no other inputs to determine whether ahazardous relationship exists between said first and second craft.
 3. Acollision avoidance system comprising: a transmitter on a first craftfor generating signals indicative of a first craft velocity vector andits altitude, means on a second craft for generating signals indicativeof a second craft velocity vector and its altitude, a directionalreceiver on a second craft for receiving said signals indicative of thefirst craft velocity vector, said receiver connected to said means ofgenerating signals indicative of a second craft velocity vector forcombining said signals to determine an approximate relative bearing ofsaid first craft from said second craft to determine the magnitude ofthe relative velocity vector, said directional receiver requiring noother inputs to calculate the approximate relative bearing of said firstcraft from said second craft, a first computing means on said secondcraft for determining a range between said first and second craft, and asecond computing means on said second craft connected to saiddirectional receiver and to said first computing mEans for comparing themagnitude of the relative velocity vector determined by said directionalreceiver to the range determined by said first computer means and forcomparing said signals indicative of the first and second craftaltitudes to determine whether a hazardous relationship exists betweensaid first and second craft, said second computer means requiring noother inputs to determine whether a hazardous relationship existsbetween said first and second craft.
 4. A collision avoidance systemcomprising: a transmitter on a first craft for generating signalsindicative of a first craft velocity vector, means on a second craft forgenerating signals indicative of a second craft velocity vector, areceiver means on the second craft for receiving said signals indicativeof the first craft velocity vector, said receiver connected to saidmeans of generating signals indicative of a second craft velocity vectorfor combining said signals by squaring their individual values andadding the squares together to obtain the square of the magnitude of arelative velocity vector, a first computing means on said second craftfor determining a range between said first and second craft, and asecond computing means on said second craft connected to said receivermeans and to said first computing means to divide the square of therelative velocity vector by a square of the range determined by saidfirst computing means and to determine whether the resultant quotient isless than a predetermined value.
 5. In a collision avoidance system, thecombination of: a transmitter generating signals indicative of therectangular components of a first craft velocity vector, a receivermeans receiving said signals indicative of rectangular components of thefirst craft velocity vector, means on said second craft for generatingsignals indicative of the rectangular components of the second craftvelocity vector, and computing means connected to said receiver meansand to said second craft signal generating means for combining themagnitudes of corresponding components indicative of the first andsecond craft velocity vectors to determine whether each said craft is apossible hazard to the other said craft, said computer means receivingno other inputs to determine whether each said craft is a possiblehazard to the other craft whenever the altitude of the two craft arewithin a predetermined relative range of each other.
 6. A system forindicating the presence of a navigational hazard comprising: atransmitter adapted to be carried by a first craft for generatingsignals having characteristics indicative of the altitude, course andvelocity of said craft, a receiver carried by said craft for receivingother signals transmitted from a second craft and having characteristicsindicative of the altitude, course and velocity of said second craft,range measuring means carried by said first craft for determining therange of said second craft, and means utilizing said signals and saidrange measuring means to indicate whether said second craft is anavigational hazard to the first craft, said means requiring no otherinputs to determine when said second craft is a navigational hazard tosaid first craft.
 7. A system for indicating the presence of anavigational hazard comprising: a transmitter adapted to be carried by afirst craft for generating signals indicating the actual altitude,course and velocity of said craft, a receiver carried by said craft forreceiving other signals transmitted from a second craft and indicatingthe actual altitude, course and velocity of said second craft, rangemeasuring means carried by said first craft for determining the range ofsaid second craft, and means utilizing said signals and said rangemeasuring means to indicate whether said second craft is a navigationalhazard to the first craft, said means requiring no other inputs todetermine when said second craft is a navigaTional hazard to the firstcraft.
 8. A computer comprising: first means for combining signalsrepresentative of a first component relative to two fixed orthogonaldatum lines of a first craft''s velocity vector and a parallel firstcomponent of a second craft''s velocity vector to obtain a signalrepresentative of a first component of a relative velocity vector havinga magnitude, second means for combining signals representative of asecond component relative to said fixed orthogonal datum lines of saidfirst craft''s velocity vector which is perpendicular to said firstcomponent and a parallel second component of said second craft''svelocity vector to obtain a signal representative of a second componentof the relative velocity vector, third means connected to said first andsecond means for obtaining a signal representative of the relativevelocity vector magnitude from the signals representative of said firstand second relative velocity vector components, and fourth means forcombining said signal representative of the relative velocity vectormagnitude with a signal representative of the range between said firstand second craft to obtain a value representative of the time to a pointof closest approach between said first and second craft, said fourthmeans requiring no other inputs to obtain the value representative ofthe time to a point of closest approach between said first and secondcraft.
 9. A computer comprising: first means for combining signalsrepresentative of a first component of a first craft''s velocity vectorand a parallel first component of a second craft''s velocity vector toobtain a signal representative of a first component of a relativevelocity vector having a magnitude, second means for combining a signalrepresentative of a second component of said first craft''s velocityvector which is perpendicular to said first component and a parallelsecond component of said second craft''s velocity vector to obtain asignal representative of a second component of the relative velocityvector, third means connected to said first and second means forobtaining a signal representative of the relative velocity vectormagnitude from the signals representative of said first and secondrelative velocity vector components, fourth means for obtaining a signalrepresentative of the range between the first and second craft, andfifth means connected to said third and fourth means for combining saidrelative velocity vector magnitude and said range to determine whethereach craft is a potential hazard to the other, said fifth meansrequiring no other inputs to determine whether each craft is a potentialhazard to the other.
 10. A computer comprising: first means forcombining a signal representative of a first component of a firstcraft''s velocity vector and a parallel first component of a secondcraft''s velocity vector to obtain a signal representative of a firstcomponent of a relative velocity vector having a magnitude, second meansfor combining a signal representative of a second component of a firstcraft''s velocity vector which is perpendicular to said first componentand a parallel second component of said second craft''s velocity vectorto obtain a signal representative of a second component of the relativevelocity vector, third means connected to said first and second meansfor obtaining a signal representative of the relative velocity vectormagnitude from the signals representative of said first and secondrelative velocity vector components, fourth means connected to saidthird means for combining said signal representative of the relativevelocity vector magnitude with a signal representative of the rangebetween said first and second craft to obtain a signal representative ofthe time to a point of closest approach between said first and secondcraft, fifth means for combining a signal indicative of the altitude ofsaid first craft with a signal indicative of the altitude of said secondcraft to determine whether said craft are within a predeterminedaltitude range of each other, and sixth means connected to said fourthand fifth means for determining whether said first and second craft area hazard to each other, said sixth means requiring no other inputs todetermine whether said first and second craft are a hazard to eachother.
 11. A computer comprising: first means for combining signalsrepresentative of a first component of a first craft''s velocity vectorand a parallel first component of a second craft''s velocity vector toobtain a signal representative of a first component of a relativevelocity vector having a direction and a magnitude, second means forcombining signals representative of a second component of said firstcraft''s velocity vector which is perpendicular to said first componentand a parallel second component of said second craft''s velocity vectorto obtain a signal representative of a second component of the relativevelocity vector, third means connected to said first and second meansfor combining the signal representative of said first relative velocityvector component with the signal representative of said second relativevelocity vector component to obtain a signal representative of therelative velocity vector direction and a signal representative of therelative velocity vector magnitude, fourth means for obtaining a signalrepresentative of the range between the first and second craft, fifthmeans connected to said third and fourth means for combining said signalrepresentative of the relative velocity vector magnitude with saidsignal representative of the range between said first and second craftto obtain a value representative of the time to a point of closestapproach between said first and second craft, said fifth means requiringno other inputs to obtain a value representative of the time to a pointof closest approach between said first and second craft, sixth means forcombining a signal indicative of the altitude of said first craft with asignal indicative of the altitude of said second craft to determinewhether said craft are within a predetermined altitude range of eachother, and seventh means for determining whether each craft is apotential hazard to the other responsive to said fifth means forobtaining a value representative of the time to a point of closestapproach and responsive to said sixth means for determining whether saidcraft are within a predetermined altitude range of each other.
 12. Acomputer comprising: first means for combining a signal representativeof a first component of a first craft''s velocity vector and a parallelfirst component of a second craft''s velocity vector to obtain a signalrepresentative of a first component of a first relative velocity vectorhaving a magnitude and a first component of a second relative velocityvector having a magnitude, second means for combining a signalrepresentative of a second component of said first craft''s velocityvector which is perpendicular to said first component and a parallelsecond component of said second craft''s velocity vector to obtain asignal representative of a second component of the first relativevelocity vector, third means connected to said first and second meansfor obtaining a signal representative of the first relative velocityvector magnitude from said signals representative of said first andsecond relative velocity vector components of said first relativevelocity vector, fourth means connected to said third means forcombining said signal representative of the first relative velocityvector magnitude with a signal representative of the range between saidfirst and second craft to obtain a signal representative of the time toa point of closest approach between said first and second craft, fifthmeans for combining a signal representative of a third component of saidfirst craft''s velocity vectoR which is perpendicular to said first andsecond components to a signal representative of a parallel thirdcomponent of said second craft''s velocity vector to obtain a signalrepresentative of a second component of the second relative velocityvector, sixth means connected to said first and fifth means forobtaining a value representative of the second relative velocity vectormagnitude from said signals representative of said first and thirdrelative velocity vector components, and seventh means connected to saidsixth means for combining said signal representative of the secondrelative velocity vector magnitude with a signal representative of therange between said first and second craft to obtain another signalrepresentative of the time to a point of closest approach between saidfirst and second craft.
 13. In combination with the computer specifiedin claim 12, an eighth means connected to said fourth and seventh meansfor determining whether the time to a point of closest approach derivedfrom said signal representative of said first relative velocity vectorand the time to a point of closest approach derived from said signalrepresentative of said second relative velocity vector are less than apredetermined interval of time.
 14. A computer comprising: first meansfor combining signals representative of a first component of a firstcraft''s velocity vector and a parallel first component of a secondcraft''s velocity vector to obtain a signal representative of a firstcomponent of a relative velocity vector having a magnitude, second meansfor combining signals representative of a second component of said firstcraft''s velocity vector which is perpendicular to said first componentand a parallel second component of said second craft''s velocity vectorto obtain a signal representative of a second component of the relativevelocity vector, third means for combining signals representative of athird component of said first craft''s velocity vector which isperpendicular to said first and second components and a parallel thirdcomponent of said second craft''s velocity vector to obtain a signalrepresentative of a third component of the relative velocity vector,fourth means connected to said first, second and third means forobtaining a value representative of the relative velocity vectormagnitude from the signals representative of said first, second, andthird relative velocity vector components, and fifth means connected tosaid fourth means for combining said signal representative of the firstrelative velocity vector magnitude with a signal representative of therange between said first and second craft to obtain a valuerepresentative of the time to a point of closest approach between saidfirst and second craft.